Orban Optimod-PC 1101, Operating Manual

Page: 138 / 258

3-18
OPERATION ORBAN MODEL 1101
We included this safety limiter for customers whose policies require the
BS.1770 loudness meter reading to be constrained below specified
threshold regardless of how loud human listeners perceive the program
to be. Our experience suggests that the BS.1770-2 meter will often over-
read material with unusually low peak-to-average ratios, like highly pro-
duced commercials and promos. Strict reliance on the BS.1770 meter can
therefore make such material sound unnaturally quiet compared to sur-
rounding material, so we prefer the sound when the CBS Loudness Con-
troller is used exclusively for loudness control.
The CBS Loudness Meter and BS.1770 Loudness Meter both receive the
signal after it has been processed by both the CBS Loudness Controller
and the BS.1770 safety limiter. Therefore, if the BS.1770 safety limiter is
producing gain reduction, the CBS Loudness Meter is likely to read lower
than 0 dB.
For a more detailed discussion of these issues, refer to Using the ITU
BS.1770 and CBS Loudness Meters to Measure Loudness Controller Per-
formance,
starting on page 3-73.
Two-Band Purist Processing
OPTIMOD-PC’s two-band algorithm can be set to be phase-linear. We believe that
this is the ideal processing for classical music and jazz programming because it does
not dynamically re-equalize high frequencies; the subtle HF limiter only acts to re-
duce high frequency energy when it would otherwise cause overload because of the
TV preemphasis curve. OPTIMOD-PC’s two-band phase-linear structure therefore
keeps the musical spectrum coherent and natural.
Input/output Delay
The input/output time delay of the processing is typically 25 ms—a bit less than an
NTSC frame. To make intelligent decisions about how to process, OPTIMOD-PC needs
to look ahead at the next part of the program waveform. As digital transmission
processing advances further and further from its analog roots, this is the inevitable
price of progress.
To avoid lip sync problems in video applications, OPTIMOD-PC allows you to pad the
delay to one full frame of 24, 25, or 29.97 fps video, which makes matching audio
and video delays convenient. See step (3.D) on page 2-23.
If talent monitors off-air through headphones that are in the same location as
OPTIMOD-PC, you can configure OPTIMOD-PC’s analog outputs to supply a special
low-delay monitor signal to drive talent headphones only. (See
Output and Routing
Switcher on page 2-39.)
Customizing OPTIMOD-PC’s Sound
See Figure 3-2: Simplified OPTIMOD-PC Digital Signal Processing Diagram on page 3-
11.